The present invention relates to an apparatus for moulding plastic containers. Apparatus of this kind have been known from the prior art for a long time. Thus, it is known to heat plastic preforms initially in heating sections and subsequently to expand them into their final bottle form using apparatus such as blow moulding machines. In such blow moulding machines, so-called stretching rods are usually also used, which stretch the containers during the expansion operation in their longitudinal direction.
From DE 33 141 06 A1, a method and an apparatus for producing hollow bodies from hot-forming plastics are known. This expansion process is carried out in two steps, wherein initially a tooling-free blowing up of the preform under application of heat is carried out and subsequently, in a main blowing process which is carried out in a further stage, the final form of the container is created. This method, which was disclosed in the above-mentioned patent application from the early 80s, has by now become obsolete in as far as usually the entire moulding process is carried out in one step, i.e. both a pre-blowing step and the actual main blowing step are carried out within the same moulding process.
In particular, meanwhile even complex bottle shapes may be achieved using this method, whilst according to DE 33 141 06 A1 the primary object was to produce containers in a complex shape from plastic preforms.
From WO 03/022551 A1, an apparatus and a method for controlling the temperature of preforms are known. Here, a temperature control unit to be introduced into the interior of the preforms is provided.
EP 0237459 B1 describes a method and an apparatus for producing containers. Here, the moulding of the plastic preform is carried out in several steps. More specifically, upon heating of the plastic preform, an intermediate container is initially formed and subsequently this intermediate container is heated and then moulded into its final shape.
More recently, however, attention has been shifted to an increasing degree on saving costs during the manufacture of such plastic containers. In particular, methods are being sought that allow the amount of materials used to be reduced. During the manufacture of these plastic containers, the plastic preforms already have their final screw thread and only the base body of the preform is stretched. For this reason it is necessary to make absolutely sure that the area of the thread is not damaged during the moulding process, otherwise it will later be impossible to attach the thread screw caps properly. With this approach, however, it is sometimes inevitable that an unstretched or comparatively thick wall area remains immediately below the so-called support ring of the container. However, this area involves an increased use of material.